Moves the SYSTEM_EMAIL_* resolution logic out of group_vars/all/03_email.yml
into a dedicated Ansible lookup plugin, so every role template reads outgoing
mail settings via lookup('email') (global) or lookup('email', application_id)
(per-app). Per-app compose.services.email is merged on top of the resolved
defaults; SYSTEM_EMAIL_* variables remain usable as an inventory escape hatch.
Also splits the email docs: administrator-facing configuration stays under
docs/administration/configuration/, plugin contract and extension rules move
to docs/contributing/design/services/email.md. services.md is relocated to
services/base.md so the services/ subtree can host per-service design pages.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
kevinveenbirkenbachandClaude Opus 4.7